It's very normal to overheat even it's stock. It depends on weather, track layout, temperature, etc. and the most critical: driving. As myself, I overheat most of stock M3's in less than 4 laps, or 3 laps for good suspension set up and tires. I know most people don't have problem with overheating. That's why driving makes huge differences.
For FI M3's, it's not gonna help much I guess.
We are having engine oil cooler for both FI and NA, tranny cooler for DCT, and power steering cooler in development. We will be finished up some time next month. But we have not yet decided to make it in production to general public. I will keep everyone updated.